1. Technical Field
The present disclosure relates to an internal combustion engine having a device for selectively deactivating one or more intake and/or exhaust valves.
2. Background Art
Conventional internal combustion engines use a camshaft-driven valvetrain to operate intake and exhaust valves that control the exchange of gases and fuel in the combustion chambers formed between the engine block and cylinder head. In overhead cam valvetrains, camshaft lobes directly drive rocker arms that actuate the valves, whereas “cam-in-block” or pushrod engines use pushrods to couple camshaft lobes to corresponding rocker arms. Relatively thin (or flat) rocker arms that pivot about a ball supported by a pedestal or fulcrum secured to the engine block have been developed to facilitate actuation of multiple valves per cylinder as disclosed in commonly owned and copending U.S. patent application Ser. No. 11/308,021 filed Mar. 3, 2006. This arrangement actuates all the associated intake/exhaust valves for each camshaft revolution.
Under various engine, vehicle, and/or ambient operating conditions it may be desirable to selectively deactivate one or more valves for one or more cylinders, i.e. to selectively prevent one or more intake and/or exhaust valves from opening either for all engine cylinders or a subset of cylinders during starting, stopping, or running of the engine. Representative applications for selective valve deactivation may include variable displacement engines or cylinder cut-off systems that operate on a subset of cylinders under selected conditions; deactivation of one intake valve on a multiple intake valve-per-cylinder engine to improve swirl motion at selected engine speeds; and deactivating valves during engine starting and/or running to vary exhaust temperature and manage operating temperature of emission treatment devices, for example.
Regardless of the particular application for a valve deactivation system, it is generally desirable to be able to reliably synchronize valve deactivation and subsequent re-activation with other engine events, such as fuel injection and piston position, for example. In addition, it is desirable for the system to not impact valvetrain performance by adding mass to moving components; to be implemented without changes to complex parts such as the cylinder block, cylinder head, or engine lubrication system; to be compact and light-weight; and to be capable of use in multiple-valve-per-cylinder gas and diesel engines.